Assaidi spent 2013-14 at the Britannia Stadium, scoring five goals in 25 appearances in all competitions.
Talks took place during the close-season over the possibility of making the switch permanent, but discussions broke down, with both Liverpool's reported £7 million asking price and the player's requested personal terms understood to have been a stumbling block.
But the 26-year-old Morocco international will now spend the rest of the current campaign with Mark Hughes' team.
Assaidi's return offers a timely boost to Hughes' attacking options amid fears that Peter Odemwingie sustained cruciate knee ligament damage during Saturday's 1-0 win at Manchester City.
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